A known cogeneration system is disclosed in JP2003-21392A (hereinafter referred to as Reference 1), for example. According to the cogeneration system disclosed, in a case where all multiple heating terminals such as floors are prevented from dissipating heat by means of a temperature adjustment function (i.e., an off state) because of a temperature increase during a heating operation, a heat exchange is conducted between hot water in a floor heating circuit and hot water in a hot water storage/supply circuit so as to store heat in the hot water storage/supply circuit (specifically, a hot water storage tank). As a result, the hot water in the floor heating circuit is prevented from reaching extremely high temperatures. In an exhaust heat circuit of a power generation unit (i.e., coolant circuit), a radiator for heat dissipation is omitted in view of energy saving.
According to the cogeneration system disclosed in Reference 1, surplus heat produced when the floors are heated (i.e., floor heating) is recovered and stored in the hot water storage tank. Thus, the hot water storage/supply circuit is inevitably provided at the cogeneration system. In this case, the hot water storage tank has generally a sufficient capacity for accommodating a hot water supply load for home usage, such as 100 liters or more, which leads to a large tank and a large space and an increased cost for installing the tank.
In addition, the heat stored in the hot water storage tank is used only for the hot water supply. Thus, when the hot water supply load is not present (i.e., the hot water supply is not required or used) for a long period of time, the surplus heat cannot be stored in the hot water storage tank. Even when a heating load is present, an operation of the cogeneration system including the power generation (usage of exhaust heat) is impossible. That is, the usage of the exhaust heat is impossible at a time of the heating operation because of an influence of the hot water supply load.
According to a different cogeneration system from that disclosed in Reference 1 such as a heat pump-type hot water supply system, a heat stored in a hot water storage tank for a hot water supply is used for heating. However, in this case, a temperature stratification within the hot water storage tank is broken by the heating operation, which leads to a decrease in energy saving and an enlargement of the system.
A need thus exists for a cogeneration system which is not susceptible to the drawback mentioned above.